Noise and vibration management is a significant issue for vehicle manufacturers, as cabin noise is a major factor in the comfort experience of automotive passengers. Therefore, noise and vibration abatement measures are routinely incorporated into motor vehicles. These abatement measures often utilize flexible polyurethane foams. However, such foams typically are called upon to perform one or more functional purpose that can not be compromised at the expense of noise and vibration absorption, for example, under the hood applications require a high degree of flame resistance, in some cases an Underwriters' Laboratories Standard 94 (UL 94) V-0 rating.
The use of fire retardants in polyurethane foams is well known. Methods of imparting flame retardancy that combine calcium carbonate, ammonium hydroxide, or another such inorganic compound, halophosphoric acid compound, melamine, or another such compound with a polyol are also known. However, a large amount of such a compound must be added to impart flame retardancy often resulting in considerable problems in relationship to the properties, moldability, economics, and the like.
Methods of making flame retardant flexible polyurethane foam can also include adding a halogenated phosphoric acid ester as a flame retardant to a composition for polyester-based polyurethane foam and using a reactive flame retardant that adds a phosphorus or halogen atom to the polyhydroxyl compound or organic polyisocyanate that is a raw material of the polyurethane foam. However, the urethane foam obtained by these methods discolors over time, the foam itself deteriorates, and adequate flame retardancy is not maintained over an extended period of time because the flame retardant volatilizes.
Due to recent environmental and market trends, non-halogenated flame retardant solutions have been pursued. For example, U.S. Pat. No. 6,765,034 discloses a flame resistant flexible polyurethane composition for use in sound deadening and vibration applications that comprises no flame retardants and relies on the selection of a specific isocyanate mixture and polyol. Furthermore, the flammability of said foams is defined only in regard to FMVSS302 flammability test, which is a less stringent flammability test as compared to the UL 94 test. FMVSS (Federal Motor Vehicle Safety Standard) 302 is a horizontal flame test which relates to a material's tendency to melt (therefore not spreading flame) as opposed to UL 94 vertical flame test which describes a material's ability to resist combustion.
US Patent Publication 20030130365 describes a process to make a flexible polyurethane foam from a rigid polyurethane foam comprising an organic phosphate flame retardant in combination with expandable graphite. However, said process is a multi-step process requiring a crushing step and a heating step. Furthermore, said polyurethane foams are evaluated by the less stringent flame spread FMVSS 302 test with no mention of UL 94 combustion resistance performance.
U.S. Pat. No. 5,169,876 discloses a flexible polyurethane foam comprising very high levels (20 to 50 weight percent) of expandable graphite incorporated into the cell walls which meet UL 94 V-0. However, the process requires a heated split stream polyol addition wherein one stream contains the expandable graphite. The high levels of expandable graphite and complex process steps contribute to an expensive product and may negatively affect the resultant foam properties, such as tensile strength.
JP 1998147623 discloses a flexible polyurethane foam with a complex flame retardant mixture comprising ammonium polyphosphate, red phosphorus and expandable graphite. However, to meet UL 94 V-2 or V-0 requirements, said foams require from 4 to 9 times the amount of ammonium polyphosphate as compared to the amount of red phosphorus.
There exists an unmet need for a flame resistant flexible polyurethane foam composition for sound deadening and vibration applications which meets UL 94 V-0 requirements, especially after exposure to elevated temperatures over a period of time and method to make said foam, that is cost effective, does not require additional multiple process steps over conventional methods, and does not require complex flame retardant mixtures and/or high levels of flame retardants.